1. Field of the Invention
The invention relates generally to high-performance communication systems and specifically to a high-speed, low-power differentiator, rectifier, mixer, and low-pass filter (DRML) circuit.
2. Description of the Related Art
Random nonreturn-to-zero (NRZ) data contains no spectral component at its fundamental data frequency (hereinafter referred to as "f"). For example, FIG. 1 illustrates a magnitude versus frequency graph illustrating random nonreturn-to-zero (NRZ) data generated at a clock frequency of 1 GHz. As illustrated in FIG. 1, the NRZ data includes spectral components at one-half the clock frequency (1/2 f), but the even harmonics have a null magnitude. Consequently, frequencies of 1/2*f, 3/2*f, 5/2*f, etc. are prevalent, but the desired 2/2*f or simply f (1 GHz) is missing.
In order to address this problem, clock recovery circuits (CRCs) are employed to extract the fundamental data frequency from a nonreturn-to-zero (NRZ) data sequence. A conventional approach for extracting the frequency f is to employ a separate differentiator circuit, a rectifier circuit, a mixer circuit and a low-pass filter circuit. An example of this approach is described in the IEEE Journal of Solid State Circuits, Vol. 31, No. 4, April 1996, entitled, "A 2.5-Gb/s 15-mW Clock Recovery Circuit", by Behzad Razavi.
However, this approach has several disadvantages. First, because each function requires a separate circuit, and each circuit is relatively complex, a large number of transistors are needed. For example, in the Razavi circuit, the differentiator alone requires four (4) transistors and the mixer circuit, alone, requires four (4) additional transistors. The large number of transistors translates to a large area requirement for the clock recovery circuit. Moreover, the conventional approach requires more DC current for operation, thereby increasing the power consumption for the circuit. Furthermore, the conventional circuits require a higher power supply voltage since the components (i.e., differentiator circuit, rectifier circuit, mixer circuit and low-pass filter) are stacked on top of each other.
Accordingly, there remains a need in the industry for an improved CRC that 1) can be implemented with fewer transistors and a reduced area, 2) reduces power consumption and 3) is adapted for low voltage operation.